The invention relates to a method for the commutation of an electronically commutated, brushless, polyphase permanent magnet motor.
Polyphase permanent magnet motors nowadays are commutated increasingly electronically, i.e. brushlessly. The rotating rotary field in the stator winding with this is electronically produced, for example by way of a voltage/frequency converter. In order to be able to optimally convert the electrical power into mechanical motor power and in order to ensure a motor running which is as low vibration, smooth and low-noise as possible, it is necessary to synchronize the speed between the electronically produced circulating rotary field of the stator and the permanent magnet or magnets circulating therein. For this a position acquirement of the rotor is required which may either be effected by sensors provided on the stator side, for example Hall sensors but also by way of acquisition of the intrinsic induction arising in the stator windings. The first requires a measurement effort which is not inconsiderable, for the acquisition as well as for evaluation. The latter however in practice is only possible with the help of a separate measurement winding or however with block-commutated motors, since a measurement of the intrinsic induction without a great effort with regard to measurement technology is only possible in the phase without supply voltage when the voltage arising by way of intrinsic induction in the motor phase winding is not superimposed by the external supply voltage.
From U.S. Pat. No. 4,654,566 it is known, by acquiring the voltage induced within a winding, to determine the rotor position and to commutate the motor in dependence of the evaluated rotor position, i.e. specifically to determine the zero crossing of the voltage induced by the intrinsic induction in a motor winding and to carry out the reapplication of this motor winding to the supply voltage at a certain angle (commutating angle) from this point on. With this method the commutating point in time is matched to the current/present rotor position in that the commutating angle or the time interval determined by way of the dependence of the rotor speed is fixed from the zero crossing of the voltage induced in a motor winding. With this the commutation is always effected in dependence on the current position, however the commutation angle is always the same. An optimization of the commutating angle may however only be effected in dependence on the rotary speed so that the commutating method known from the above mentioned US patent can only be usefully applied when the motor is operated at a constant rotational speed.